In this paper we have investigated Bragg fibers for the 1.94 μm laser- radiation delivery generated by a thulium fiber laser with a maximal continuous output power 50W. For such investigation laboratory-designed and fabricated hollow-core Bragg fibers have been employed with different diameters of 5, 40, 56 and 73 μm surrounded by three pairs of circular Bragg layers. Fundamental optical characteristics such as overall transmittance, attenuation coefficient, bending losses, and delivered spatial beam profiles at the wavelength of 1.94 μm for all tested fibers are reported and summarized in this contribution. In the case of laser radiation delivery with the intensity of 65 kW/cm2, the lowest attenuation coefficient of 1.278 dB/m was determined for the Bragg fiber with the inner air-core diameter of 56 μm. Moreover, the bending losses for a small bend diameter of 15 mm reached 0.177 dB only. However delivered laser radiation was highly multimode character.

Ondřej Podrazký, Institute of Photonics and Electronics of the ASCR, v.v.i. (Czech Republic)Ivan Kašík, Institute of Photonics and Electronics of the ASCR, v.v.i. (Czech Republic)Vlastimil Matějec, Institute of Photonics and Electronics of the ASCR, v.v.i. (Czech Republic)